CN105388457A - Long-baseline hydroacoustic positioning method based on equivalent acoustic velocity gradient - Google Patents

Abstract

The invention discloses a long-baseline underwater acoustic positioning method based on an equivalent sound velocity gradient, which belongs to the field of underwater acoustic positioning and navigation, and adopts a long-baseline underwater acoustic positioning system, which transmits positioning signals by a transceiver transducer mounted on a target , the transponder array arranged on the seabed receives and returns the response signal, measures the propagation time of the acoustic signal from launch to return, and the sound velocity value is measured in real time by the miniature sound velocity meter installed on the transceiver transducer and the subsea transponder; according to the equivalent The principle of the sound velocity profile, using the historical sound velocity profile to calculate the initial value to search for the equivalent sound velocity gradient, when the round-trip propagation distance from the transducer to the transponder and from the transponder to the transducer is equal, determine the equivalent sound velocity gradient value, and calculate the accuracy of the target Location. The present invention does not need accurate sound velocity profile, even does not need sound velocity profile, effectively eliminates the influence of representative error of sound velocity profile, and improves the accuracy of underwater target positioning.

Description

A Long Baseline Acoustic Positioning Method Based on Equivalent Sound Velocity Gradient

technical field

The invention belongs to the field of underwater acoustic positioning and navigation, and in particular relates to a long baseline underwater acoustic positioning method based on an equivalent sound velocity gradient.

Background technique

The long-baseline hydroacoustic positioning system has a large tracking range and high positioning accuracy, and has been widely used in marine resource development, marine engineering construction, underwater archaeology, and marine national defense construction. The long-baseline underwater acoustic positioning systems that have been developed so far mostly use the positioning method of distance intersection. The accuracy of distance measurement directly affects the positioning accuracy of the long-baseline system. Therefore, it is very important to correct the sound ray based on the measured sound velocity profile, but the sound velocity profile is difficult to obtain in real time. , the representative error of the sound velocity profile is unavoidable, so it is necessary to study a long baseline underwater acoustic positioning system that can effectively eliminate the influence of the representative error of the sound velocity profile.

Contents of the invention

Aiming at the above technical problems existing in the prior art, the present invention proposes a long baseline underwater acoustic positioning method based on the equivalent sound velocity gradient, which is reasonably designed, overcomes the deficiencies of the prior art, eliminates the error influence of the sound velocity profile, and improves accuracy.

In order to achieve the above object, the present invention adopts the following technical solutions:

A long-baseline underwater acoustic positioning method based on an equivalent sound velocity gradient, using a long-baseline underwater acoustic positioning system, which includes a processing and control unit installed on a surface vessel, a transceiver transducer installed on a surface vessel or an underwater robot, and A transponder array composed of a plurality of transponders arranged on the seabed, and a miniature sound velocity meter is installed on the transceiver transducer and the transponder array;

The long baseline underwater acoustic positioning method based on the equivalent sound velocity gradient is carried out according to the following steps:

Step 1: Calibrate the absolute position of the transponder array deployed on the seabed;

Step 2: Measure the round-trip time t _i of sound wave propagation by controlling the transceiver transducer and the transponder matrix through the processing and control unit, and measure the sound velocity C ₀ of the transceiver transducer and the sound velocity of the transponder by controlling the miniature sound velocity meter through the processing and control unit C′ _0i ;

Step 3: Calculating the approximate distance and approximate coordinates of the target from the transponder to each transponder and the approximate distance and approximate coordinates of the target from each transponder to the transponder;

Step 4: Calculate the exact target position.

Preferably, in step 3, it specifically includes:

Step 3.1: Calculate the approximate equivalent sound velocity gradient g ₀ using the historical sound velocity profile, set the search step size Δg, and search for the equivalent sound velocity gradient g _ij :

g _ij =g ₀ +j·Δg(9)

In the formula, i is the serial number of the sound ray, and j is the number of searches.

Step 3.2 _: Calculate the approximate distance L _ij from the transceiver transducer to each transponder and the approximate _target coordinates P _j (X _j , _{Y j} , Z _j );

Step 3.3: According to the principle of equal sound velocity section integral area, calculate the equivalent sound velocity gradient g′ _ij from the transponder to the transceiver transducer by formula (10):

g' _ij =g _ij -2(C' _0i -C ₀ )/(Z _i -Z _j )(10)

Among them, C ₀ and C′ _0i are the sound velocity values of the transceiver transducer and the transponder measured by the micro-sound velocity meter, Z _i is the depth value of the transponder, and Z _j is the approximate target coordinate P _j calculated in step 3.2 Depth value of (X _j ,Y _j ,Z _j );

Step 3.4: Calculate the approximate distance L′ _ij from each transponder to the transceiver transducer and the approximate coordinates P′ _j of the target by using the calculated g′ _ij and the measured sound velocity C′ _0i of the transponder and the round-trip time t _i of the sound wave (X′ _j , Y′ _j , Z′ _j ).

Preferably, in step 4, specifically include:

Step 4.1: According to the calculated distance L _ij from the transceiver transducer to each transponder and the distance L′ _ij from each transponder to the transceiver transducer, let ΔL _ij =|L _ij -L' _ij |;

Step 4.2: According to the principle of equal round-trip distance, the g _ij value when ΔL _ij takes the minimum value is the actual equivalent sound velocity gradient g _i value, that is, g _i = g _ij , and the accurate target position P is calculated by the least square method (X,Y,Z).

Beneficial technical effects brought by the present invention:

The present invention proposes a long baseline underwater acoustic positioning method based on the equivalent sound velocity gradient. Compared with the prior art, the accurate sound velocity profile may not be required, or even the sound velocity profile is not required, and the representative error of the sound velocity profile has no effect on the positioning calculation accuracy. The impact of the long baseline hydroacoustic positioning system improves the positioning accuracy.

Description of drawings

Fig. 1 is a schematic diagram of the long baseline underwater acoustic positioning system in the long baseline underwater acoustic positioning method based on the equivalent sound velocity gradient of the present invention.

Fig. 2 is a flowchart of the long baseline underwater acoustic positioning method based on the equivalent sound velocity gradient of the present invention.

Fig. 3 is a schematic diagram of calculating the equivalent sound velocity gradient in the present invention.

Fig. 4 is a diagram of the relationship between the equivalent sound velocity gradient and the distance difference in the present invention.

Fig. 5 is a schematic diagram of the submarine transponder array and target positions in the present invention.

Fig. 6 is a graph showing the relationship between the search sound velocity gradient change and the distance difference in the present invention.

Fig. 7 is a comparison diagram of positioning errors between the method of the present invention and other methods.

Among them, 1-processing and control unit; 2-receiver transducer; 3-transponder; 4-miniature sound velocity meter.

detailed description

Below in conjunction with accompanying drawing and specific embodiment the present invention is described in further detail:

As shown in Figure 1, the long-baseline hydroacoustic positioning system includes a processing and control unit 1 installed on a surface vessel, a transceiver transducer 2 installed on a vessel or an underwater robot, and multiple transponders 3 deployed on the seabed. The composed transponder array, the transponder 2 and the transponder 3 are all equipped with a miniature sound velocity meter 4 .

The processing and control unit 1 is responsible for the storage and calculation of measurement data, and controls the operation of the entire system.

The processing and control unit 1 controls the transceiving transducer and the transponder array to measure the round-trip time t _i of sound wave propagation, and controls the miniature sound velocity meter to measure the sound velocity C ₀ of the transceiving transducer and the sound velocity C′ _0i of the transponder, and then measure The data t _i , C ₀ and C′ _0i are stored in the processing and control unit 1 .

Since seawater is a non-uniform medium, the speed of sound in seawater changes with temperature, salinity and pressure, and the propagation path of sound waves in seawater is a continuous curve. According to the principle of equivalent sound velocity profile method, the actual sound velocity can be The profile is replaced by a constant gradient equivalent sound velocity profile. According to the theory of ray acoustics, the trajectory of sound rays in the constant gradient layer is an arc, and the radius of the arc is:

R＝1/|pg|(1)

In the formula, g is the sound velocity gradient value in the constant gradient layer, and p is the snell constant.

g=(C _r -C ₀ )/(Z _r -Z ₀ )(2)

p=sinθ ₀ /C ₀ =sinθ _r /C _r (3)

In the formula, C ₀ is the initial sound velocity value, which can be measured by a miniature sound velocity meter installed on the transducer; C _r is the end sound velocity value, which is calculated by formula (2) when the sound velocity gradient g is known; Z ₀ is the water entry depth of the transducer, Z _r is the water depth at the transponder; θ ₀ and θ _r are the initial incident angle and end incident angle of the sound wave respectively, θ ₀ can be calculated by formula (4) through Newton’s iterative formula, θ _r can be calculated by Formula (5) is calculated to get:

tan[arcsin(C _r sinθ ₀ /C ₀ )/2]-e ^tg/2 tan(θ ₀ /2)＝0(4)

θ _r =2arctan(e ^tg/2 tan(θ ₀ /2))(5)

In the formula, t is the round-trip time of the measured sound wave, and g is the equivalent sound velocity gradient value.

The formulas for calculating the vertical distance Δz and lateral distance Δx of sound wave propagation are as follows:

$\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; R</span>}{\mathrm{<span\; class="notranslate">\; sin\&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; R</span>}{\mathrm{<span\; class="notranslate">\; sin\&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\\ \mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; R</span>}{\mathrm{<span\; class="notranslate">\; cos\&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; R</span>}{\mathrm{<span\; class="notranslate">\; cos\&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

Formula (6) is the sound ray refraction correction formula, and the corrected distance can be expressed as:

${\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&Delta;z</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

Assuming that there are 4 submarine transponders, L _i can be used to solve the positioning by using the least square method:

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Y</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Z</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\\ {\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Y</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Z</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\\ {\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Y</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Z</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\\ {\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Y</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Z</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

In the formula, P(X,Y,Z) is the coordinates of the transceiver transducer, P _i (X _i ,Y _i ,Z _i ), (i=1,2,3,4) is the Coordinates of the calibrated transponder.

In the case that the actual equivalent sound velocity gradient g _i , (i=1, 2, 3, 4) is known, the coordinates of the target transducer can be obtained through iterative calculation using formulas (1)-(8). However, since the real-time sound velocity profile is difficult to obtain, usually only the approximate equivalent sound velocity gradient g ₀ from the transducer to the transponder can be calculated by using the historical sound velocity profile. If g ₀ is directly used for calculation, the representative error of the sound velocity profile will inevitably be introduced.

The present invention uses the approximate equivalent sound velocity gradient g ₀ , sets the search step size Δg, and searches for the equivalent sound velocity gradient g _ij :

g _ij =g ₀ +j·Δg(9)

In the formula, i is the serial number of the sound ray, and j is the number of searches.

Using g _ij and the measured sound velocity C ₀ of the transceiver transducer and the sound round-trip time t _i , the approximate distance L _ij from the transceiver transducer to each transponder and the approximate target coordinates P _j (X _j ,Y _j , Z _j );

Combined with Fig. 3, according to the principle of equal sound velocity section integral area, from the equivalent sound velocity gradient g _{ij from the transducer to the transponder, the equivalent sound velocity gradient g′ ij from} the transponder to the transducer is inversely calculated:

g' _ij =g _ij -2(C' _0i -C ₀ )/(Z _i -Z _j )(10)

Among them, C ₀ , C′ _0i are the sound velocity values of the transmitting and receiving transducers and the transponder measured by the miniature sound velocity meter, Z _i is the depth value of the transponder, and Z _j is the approximate target coordinate P _j (X _j ,Y _j , Z _j );

Similarly _, the approximate distance L′ _{ij and} the approximate coordinates P _{′ j (} X′ _j , Y′ _j , Z′ _j ).

According to the principle of equal round-trip distance, L _ij and L' _ij should be equal, that is, the distance is poor ΔL _ij =|L _ij -L' _ij |=0, but if there is an error in the searched equivalent sound velocity gradient g _ij , then ΔL _ij ≠0, and the greater the g _ij error, the greater the distance difference ΔL _ij . As shown in Figure 4, the relationship between the equivalent sound velocity gradient and the distance difference, when the search equivalent sound velocity gradient reaches 0.05, that is, the search equivalent sound velocity gradient is equal to the actual equivalent sound velocity gradient, at this time ΔL _ij =0.

According to this characteristic, the equivalent sound velocity gradient g _i from the transducer to each transponder can be obtained by searching, and then the accurate target position P(X,Y,Z) can be calculated by formulas (1)～(8) .

A long baseline underwater acoustic positioning method (as shown in Figure 2) based on the equivalent sound velocity gradient of the present invention is carried out according to the following steps:

Step 1: Calibrate the absolute position of the transponder matrix deployed on the seabed, measure the round-trip time t _i of sound wave propagation by controlling the transceiver transducer and the transponder matrix through the processing and control unit, and control the miniature sound velocity meter through the processing and control unit Measure the sound velocity C ₀ of the transceiver transducer and the sound velocity C′ _0i of the transponder, and use GNSS to measure the position coordinates of the transceiver transducer; the sound ray correction method for the distance L _i between the transceiver transducer and the transponder , which is consistent with the method used to locate the target;

Step 2: Measure the round-trip time t _i of sound wave propagation by controlling the transceiver transducer and the transponder matrix through the processing and control unit, and measure the sound velocity C ₀ of the transceiver transducer and the sound velocity of the transponder by controlling the miniature sound velocity meter through the processing and control unit C′ _0i ;

Step 3: Use the historical sound velocity profile to calculate the approximate equivalent sound velocity gradient g ₀ , search for the equivalent sound velocity gradient g _ij from the transducer to the transponder within a certain range, calculate the distance L _ij from the transducer to each transponder, and target approximation Coordinate P _j (X _j , Y _j , Z _j ), inversely calculate the equivalent sound velocity gradient g′ _ij from the transponder to the transducer, calculate the distance L′ _ij from the transponder to the transducer and the approximate coordinates of the target P′ _j (X′ _j ,Y′ _j ,Z′ _j );

Step 4: According to the calculated distance L _ij from the transceiver transducer to each transponder and the distance L′ _ij from each transponder to the transceiver transducer, set ΔL _ij =|L _ij -L' _ij |; according to the round-trip distance Based on the principle of equality, judge whether ΔL _ij =|L _ij -L' _ij | can take the minimum value;

If: the judgment result is that ΔL _ij =|L _ij -L' _ij | can take the minimum value, then the g _ij value when ΔL _ij takes the minimum value is the actual equivalent sound velocity gradient g _i value, that is g _i =g _ij , using the least square method to calculate the accurate target position P(X,Y,Z);

Or if the judgment result is that ΔL _ij =|L _ij -L' _ij | cannot obtain the minimum value, then step 3 is performed.

The method of the present invention is carried out computer simulation, in conjunction with shown in Fig. 5, in the certain sea area that is 500m in depth of water, be the square grid shape of 500m to lay out the submarine sound base array by side length, the depth of target is 100m, and the speed of sound is 1500m/s, The equivalent sound velocity gradients from the target to the four transponders are 0.04, 0.05, 0.06, and 0.07 respectively, the measurement accuracy of the miniature sound velocity meter is 0.02m/s, and the calibration accuracy of the transponder array is 20cm in the plane direction and 20cm in the vertical direction. Assuming that the equivalent sound velocity gradient calculated by using the historical sound velocity profile is 0.04, and a sound velocity profile is measured in the survey area, the equivalent sound velocity gradient is 0.05. The method of the present invention is used for positioning calculation of underwater targets, and at the same time, the historical sound velocity profile and the actual measurement sound velocity profile are respectively used for positioning calculation, and the positioning accuracy of the three methods is compared and analyzed.

When the target is in a different position, the method of the present invention is used to calculate the positioning of the target, and the relationship between the search sound velocity gradient and the distance difference is obtained, as shown in Figure 6, and the final determined equivalent sound velocity gradients from the target to the four transponders are respectively 0.0395 .

As shown in Figure 7, it can be seen that the plane error and vertical error calculated by the method of the present invention are all at the decimeter level, wherein the average plane error is 0.2m, and the average vertical error is 0.1m; the historical sound velocity profile is used for positioning During the calculation, the average plane error is 1.8m, and the average vertical error is 1.3m; when the actual measured sound velocity profile is used for positioning calculation, the average plane error is 1.7m, and the average vertical error is 0.5m.

Therefore, compared with the method using the historical sound velocity profile, the use of the actual measurement of the sound velocity profile improves the accuracy of positioning calculations, but cannot eliminate the influence of the representative error of the sound velocity profile, and the long baseline underwater acoustic positioning method proposed by the present invention does not require accurate The sound velocity profile, even without the sound velocity profile, effectively eliminates the influence of the representative error of the sound velocity profile, and improves the accuracy of long baseline underwater acoustic positioning.

Of course, the above descriptions are not intended to limit the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or replacements made by those skilled in the art within the scope of the present invention shall also belong to the present invention. protection scope of the invention.

Claims (3)

1. A long-baseline underwater acoustic positioning method based on an equivalent sound velocity gradient, using a long-baseline underwater acoustic positioning system, which includes a processing and control unit installed on a surface vessel, and a transceiver installed on a surface vessel or an underwater robot A transponder and a transponder array composed of multiple transponders arranged on the seabed, and a miniature sound velocity meter is installed on the transceiver transducer and the transponder array; It is characterized in that: the long baseline underwater acoustic positioning method based on the equivalent sound velocity gradient is carried out according to the following steps: Step 1: Calibrate the absolute position of the transponder array deployed on the seabed; Step 2: Measure the round-trip time t _i of sound wave propagation by controlling the transceiver transducer and the transponder matrix through the processing and control unit, and measure the sound velocity C ₀ of the transceiver transducer and the sound velocity of the transponder by controlling the miniature sound velocity meter through the processing and control unit C′ _0i ; Step 3: Calculating the approximate distance and approximate coordinates of the target from the transponder to each transponder and the approximate distance and approximate coordinates of the target from each transponder to the transponder; Step 4: Calculate the exact target position. 2. The long baseline underwater acoustic positioning method based on equivalent sound velocity gradient according to claim 1, characterized in that: in step 3, specifically comprising: Step 3.1: Calculate the approximate equivalent sound velocity gradient g ₀ using the historical sound velocity profile, set the search step size Δg, and search for the equivalent sound velocity gradient g _ij : g _ij =g ₀ +j·Δg(9) In the formula, i is the serial number of the sound ray, and j is the number of searches. Step 3.2 _: Calculate the approximate distance L _ij from the transceiver transducer to each transponder and the approximate _target coordinates P _j (X _j , _{Y j} , Z _j ); Step 3.3: According to the principle of equal sound velocity section integral area, calculate the equivalent sound velocity gradient g′ _ij from the transponder to the transceiver transducer by formula (10): g' _ij =g _ij -2(C' _0i -C ₀ )/(Z _i -Z _j )(10) Among them, C ₀ and C′ _0i are the sound velocity values of the transceiver transducer and the transponder measured by the micro-sound velocity meter, Z _i is the depth value of the transponder, and Z _j is the approximate target coordinate P _j calculated in step 3.2 Depth value of (X _j ,Y _j ,Z _j ); Step 3.4: Calculate the approximate distance L′ _ij from each transponder to the transceiver transducer and the approximate coordinates P′ _j of the target by using the calculated g′ _ij and the measured sound velocity C′ _0i of the transponder and the round-trip time t _i of the sound wave (X′ _j , Y′ _j , Z′ _j ). 3. The long baseline underwater acoustic positioning method based on equivalent sound velocity gradient according to claim 1, characterized in that: in step 4, specifically comprising: Step 4.1: According to the calculated distance L _ij from the transceiver transducer to each transponder and the distance L′ _ij from each transponder to the transceiver transducer, set ΔL _ij =|L _ij -L′ _ij |; Step 4.2: According to the principle of equal round-trip distance, the g _ij value when ΔL _ij takes the minimum value is the actual equivalent sound velocity gradient g _i value, that is, g _i = g _ij , and the accurate target position P is calculated by the least square method (X,Y,Z).